A monitoring study was conducted on the Sandusky River, in north-central Ohio, to characterize changes in water quality and quantity before and after the removal of a low-head dam (St. John). Short-term time series of flow and turbidity were taken during the dewatering and the removal of the dam in order to determine sediment loads. High resolution spatial data, based on vertical profiles and longitudinal surveys, were collected before and after the removal to determine changes in temperature, dissolved oxygen (DO), pH, turbidity, specific conductivity, and oxidation-reduction potential (ORP) in the 18 km reservoir. Surface water samples were collected upstream and downstream of the dam before and after removal and analyzed for nitrate, ammonia, and phosphate. After dam removal, denitrification potential was studied within the former reservoir to compare the potential in newly exposed mudflats with the riverbed and the floodplain.